1. Field of the Invention
The present invention relates generally to a method for transmitting data in underground mines and more particularly to a method which utilizes burst transmission of digitally encoded radio signals transmitted by inductive coupling of a transmitter and a receiver to utility conductors and natural wave guide seams using electrically short magnetic dipole antennas.
2. Description of the Prior Art
An elementary experimental data telemetry system for use in a coal mine is briefly described by Dobroski and Stolarczyk in Control and Monitoring via Medium-Frequency Techniques and Existing Mine Conductors, IEEE Transactions On Industry Applications, vol. IA-21, Jul./Aug. 1985, p. 1091. This system utilizes spontaneous short bursts of digitally encoded medium frequency radio signals transmitted through electrical conductors existing in the mine. The paper teaches the use of line couplers as a means of coupling signals onto the local wiring. The type of sensor used for data collection was not described. Nor was a method given for avoiding data collision when transmissions occur simultaneously from several sensors or of using repeaters to communicate between surface and remote points in underground mines. Additionally, polling techniques were not described.
The features of a multiple point wireless data transmission system are described more completely in a proprietary technical proposal prepared by L. Stolarczyk and J. Jackson, entitled "Long and Short Range Multiple Point Wireless Sensor Data Transmission System", dated Nov. 7, 1986. This proposal discloses the use of high and low magnetic moment transmitters, spontaneous burst transmission techniques, the use of a sleep-timer interface circuit and the use of tuned loop antennas to inductively couple utility conductors and natural wave guide modes. Polling techniques, however, were not described.
In U.S. Pat. No. 4,753,484, issued to L. G. Stolarczyk on Jun. 28, 1988, the use of a coal rock sensor to remotely control a cutting machine was described.
U.S. Pat. No. Re. 32,563, issued to L. G. Stolarczyk for "Continuous Wave Medium Frequency Signal Transmission Survey Procedure For Imaging Structure In Coal Seams" (Stolarczyk '563), describes the use of tuned loop antennas to excite the coal seam transmission mode. In Stolarczyk '563, medium frequency radio waves are used to create images of geological anomalies occurring in coal seams.
In U.S. Pat. No. 4,742,305, issued to L. G. Stolarczyk for "Method for Constructing Vertical Images of Anomalies in Geological Formations", the technique of Stolarczyk '563 was extended to include imaging in a vertical plane and the use of tuned loop antennas to excite the natural coal seam mode of transmission was further described.
The fact that in the vicinity of a magnetic dipole, little energy is dissipated because the wave impedance is imaginary, is described by J. R. Wait in "Antenna Theory", McGraw Hill Book Co., Chapter 24, (R. E. Collin and F. S. Zucker editors, 1969).
The relationship between the current induced in a utility conductor and the electric field is described by R. F. Harrington in "Time-Harmonic Electromagnetic Field", McGraw Hill Book Co., p. 234 (1961).